(6) Hardness of steel and effects of baking

Effects of baking vary with the hardness of the steel alloy material to be treated. The baking is less effective on harder material, where softer material returning better results. This is said to be contributed not by the hydrogen being purged out of the steel, but by the diffusive migration of the hydrogen from the material's surface region to the inner region, lowering the surface hydrogen concentration to below destructive limits.
For bright zinc plating and cadmium plating, the baking is effective for low hydrogen embrittlement susceptible steel alloy with hardness of HRC40 and below. But not so with steel material with hardness of HRC46 and above.
For material that are carburized, the baking treatment is effective since only the surfaces are hard. It is thought that the occluded hydrogen would heat-diverge into the inner region of the material, and the surface hydrogen content will fall below the destructive limits. However, the hydrogen still remains within the material and may diffusively migrate to regions where stress may be concentrated if any tensile stress is applied.

(7) Summary of Baking Process

Effects of baking processes on plated products are as follows.

	1.	Removal efficiency of the hydrogen occluded during the pre-plating processes is low.
	2.	Baking process is highly effective against the occluded hydrogen during plating processes.
	3.	Effects of baking depends on the hydrogen permeability of the coating. The effects are more pronounced on coatings with coarse-crystalline structure, with pours and cracks.
	4.	Baking is less effective on thick coating layers.
	5.	Baking effectiveness is lower at lower baking temperatures.
	6.	Baking effectiveness is high with steel material with low hydrogen embrittlement susceptibility.
	7.	Post plating sit-out time duration requirement would depend on the thickness of the material. Thin plates are not affected.
	8.	Baking will cause diffusive migration of the hydrogen into the inner region of the material.
	9.	Chromating is to be applied after the baking process. If the baking is applied after the chromate coating process, the chromate coat cracks due to dehydration and the anti-corrosive properties will be degraded.